one thing i have found in single pvp outside arenas is that to be really successful its a matter of timing.
rogues seem to be about stealth and then a sudden attack before vanishing quickly as posssible , so i wait for a moment of weakness or distraction.
a shadow priest one level higher than me was fighting a mob so i watched and waited.
she instantly started a fight with another two mobs and the moment she used her psychic scream she was dead.
normally i would have just left alone but this being STV and horde ganking alliance being terrible in my realm , in STV at the present time , i decided on no mercy.
i tried taking down another rogue in the arathi highlands but they did what i do , hit vanish and disappear.
at present i am sticking with mostly subtlety , i have improved stealth and movement and an instant cooldown on vanish and sprint , might get enhanced perception too?